From patchwork Wed May 19 00:07:03 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Jeffery X-Patchwork-Id: 443752 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0B00EC43461 for ; Wed, 19 May 2021 00:07:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DFAA061360 for ; Wed, 19 May 2021 00:07:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232153AbhESAIs (ORCPT ); Tue, 18 May 2021 20:08:48 -0400 Received: from new1-smtp.messagingengine.com ([66.111.4.221]:36143 "EHLO new1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244079AbhESAIr (ORCPT ); Tue, 18 May 2021 20:08:47 -0400 Received: from compute6.internal (compute6.nyi.internal [10.202.2.46]) by mailnew.nyi.internal (Postfix) with ESMTP id DB98D580606; Tue, 18 May 2021 20:07:28 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute6.internal (MEProxy); Tue, 18 May 2021 20:07:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=aj.id.au; h=from :to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; s=fm2; bh=qbFwjze46/G9L HZQ1bh1SZv0oKRVk2i2WcEWwa8CGts=; b=i8j2NcpFjmVgKwQKuI5AkOUR3RZvq Z/vnk56+F79Zdk+o6m/LDR8c6Pe6j0P5/AZE9W4cU511/qtuSFfdmJHSJuHyRaci 8wwdLgXbeO9tWVL4ocz+GQ5DnLsMGWELLWKaHOanjPvuovrTKIRMc5QXWoLeaE2X 257unsR+BiJyKuA0FuRLHL4ekCzx5EQTXbve+Ru7sgwWNrlbPP/1OOPZOZdsU6Uc 6u2ke6hYiZLR5Ajdbm+40iNRHMwg5c6EOfMkBJviH+QZyei0cdFekMUGqbgssioX apTv2i3bopYFxTyg3DINgqGIP5eIHQnglqigELQxLjcKZBj88aQSvCF8A== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:date:from :in-reply-to:message-id:mime-version:references:subject:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm2; bh=qbFwjze46/G9LHZQ1bh1SZv0oKRVk2i2WcEWwa8CGts=; b=o+6g8Gpi kHi3XQXfiKtFWcFOgI8h11TLr3N4tLZsQQGVzZIllMdgvywz7yC4WCY4oPEOPNMs GnEnglxwKJB26jqq/7nZk7xnmVLNbG2XTmgjL/vPTKHRj2fMCe+vqua4pgy3PKPm j/izRfQjyXOkVkfy5WaPUSvAJKHCcygct+4AUBe3Prq2hjjG9f/XokAYAhxRMelq gDRbpecYGdI8d8Q63Y1TCCrEjIfdiS6Mg9sSQs11oKJllVmx5wM+SGv0KipgiklD 0UCM1zKjWfrXe9fLb8kdu2osw+iGau59nW/IZAg6exQWarbKVnXh38fQYSYvv5sK 0VhkE+ePfvXfLg== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeduledrvdeikedgvdejucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhephffvufffkffojghfggfgsedtkeertdertddtnecuhfhrohhmpeetnhgurhgv ficulfgvfhhfvghrhicuoegrnhgurhgvfiesrghjrdhiugdrrghuqeenucggtffrrghtth gvrhhnpeehhfegffehvefhieejkedtvedvlefhgfeufedtgfetueevtedvffduffelleef heenucffohhmrghinhepphhorhhtrdguvghvnecukfhppedvtdefrdehjedrvdduhedrke enucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpegrnhgu rhgvfiesrghjrdhiugdrrghu X-ME-Proxy: Received: from mistburn.lan (203-57-215-8.dyn.iinet.net.au [203.57.215.8]) by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 18 May 2021 20:07:23 -0400 (EDT) From: Andrew Jeffery To: linux-serial@vger.kernel.org Cc: gregkh@linuxfoundation.org, jirislaby@kernel.org, joel@jms.id.au, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-aspeed@lists.ozlabs.org, openbmc@lists.ozlabs.org, jenmin_yuan@aspeedtech.com, ryan_chen@aspeedtech.com, miltonm@us.ibm.com, ChiaWei Wang Subject: [PATCH v2 1/2] serial: 8250: Add UART_BUG_TXRACE workaround for Aspeed VUART Date: Wed, 19 May 2021 09:37:03 +0930 Message-Id: <20210519000704.3661773-2-andrew@aj.id.au> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210519000704.3661773-1-andrew@aj.id.au> References: <20210519000704.3661773-1-andrew@aj.id.au> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Aspeed Virtual UARTs directly bridge e.g. the system console UART on the LPC bus to the UART interface on the BMC's internal APB. As such there's no RS-232 signalling involved - the UART interfaces on each bus are directly connected as the producers and consumers of the one set of FIFOs. The APB in the AST2600 generally runs at 100MHz while the LPC bus peaks at 33MHz. The difference in clock speeds exposes a race in the VUART design where a Tx data burst on the APB interface can result in a byte lost on the LPC interface. The symptom is LSR[DR] remains clear on the LPC interface despite data being present in its Rx FIFO, while LSR[THRE] remains clear on the APB interface as the host has not consumed the data the BMC has transmitted. In this state, the UART has stalled and no further data can be transmitted without manual intervention (e.g. resetting the FIFOs, resulting in loss of data). The recommended work-around is to insert a read cycle on the APB interface between writes to THR. Cc: ChiaWei Wang Signed-off-by: Andrew Jeffery --- drivers/tty/serial/8250/8250.h | 1 + drivers/tty/serial/8250/8250_aspeed_vuart.c | 1 + drivers/tty/serial/8250/8250_port.c | 10 ++++++++++ 3 files changed, 12 insertions(+) diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h index 52bb21205bb6..34aa2714f3c9 100644 --- a/drivers/tty/serial/8250/8250.h +++ b/drivers/tty/serial/8250/8250.h @@ -88,6 +88,7 @@ struct serial8250_config { #define UART_BUG_NOMSR (1 << 2) /* UART has buggy MSR status bits (Au1x00) */ #define UART_BUG_THRE (1 << 3) /* UART has buggy THRE reassertion */ #define UART_BUG_PARITY (1 << 4) /* UART mishandles parity if FIFO enabled */ +#define UART_BUG_TXRACE (1 << 5) /* UART Tx fails to set remote DR */ #ifdef CONFIG_SERIAL_8250_SHARE_IRQ diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c index a28a394ba32a..4caab8714e2c 100644 --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c @@ -440,6 +440,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev) port.port.status = UPSTAT_SYNC_FIFO; port.port.dev = &pdev->dev; port.port.has_sysrq = IS_ENABLED(CONFIG_SERIAL_8250_CONSOLE); + port.bugs |= UART_BUG_TXRACE; rc = sysfs_create_group(&vuart->dev->kobj, &aspeed_vuart_attr_group); if (rc < 0) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index d45dab1ab316..9d44b2b2ff18 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1809,6 +1809,16 @@ void serial8250_tx_chars(struct uart_8250_port *up) count = up->tx_loadsz; do { serial_out(up, UART_TX, xmit->buf[xmit->tail]); + if (up->bugs & UART_BUG_TXRACE) { + /* The Aspeed BMC virtual UARTs have a bug where data + * may get stuck in the BMC's Tx FIFO from bursts of + * writes on the APB interface. + * + * Delay back-to-back writes by a read cycle to avoid + * stalling the VUART. + */ + (void)serial_in(up, UART_SCR); + } xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1); port->icount.tx++; if (uart_circ_empty(xmit))